It is known to insert a central venous pressure catheter into a central vein near the heart of a patient. Properly locating the end of such a catheter is important. The use of an ECG electrode at the end of the catheter to assist during the insertion and proper location of such a catheter is a standard procedure. By monitoring the ECG lead signal produced by such an ECG electrode, the end of the catheter may be accurately placed in the appropriate location, while minimizing risks from improper location.
In the past, ECG leads were removed from standard positions on the patient and connected to the ECG electrode at the end of the catheter. In particular, the right arm (RA) lead was often used for this purpose. But using this lead for inserting and locating the catheter impaired the derivation of the Einthoven ECG lead signals because the RA lead is now located in the central vein location and not on the right arm. Further, various other alarms and other calculations (arrhythmia detection, ST measurement, etc.) are distorted.
Further, in normal ECG operation, one limb signal (e.g. the right leg RL signal) is used to provide a reference potential (neutral or ground), and the remaining are coupled to a reference point (termed the Wilson Star point) through respective impedances. This reference point is coupled in common to respective input terminals of a plurality of differential amplifiers. Chest electrodes (e.g. V1, V2, V3, V4, V5, V6) are coupled to respective second input terminals of the plurality of differential amplifiers. The signals from the differential amplifiers are processed to generate ECG chest lead signals. The ECG chest lead signals are displayed by being printed out on a chart recorder and/or displayed on a display device.
However, the intra-cardiac ECG lead signal is the difference between the signal from the ECG electrode at the end of the catheter and a limb signal, typically the left leg LL signal. This requires a re-wiring of the ECG signal processor, or produces a distorted intra-cardiac ECG lead signal.
A system which permits a chest lead electrode conductor to be connected to an ECG electrode at the end of a central venous catheter, which produces an accurate intra-cardiac ECG signal, and which does not require moving of the other ECG electrodes already applied to the patient is desirable.